What is the difference between coaxiality in GB and other national standards in China?

Discussion on the standard and technology of turbine flowmeter Firstly, the working principle and structural characteristics of TGM series turbine flowmeter developed by Shanghai Aofei Gas Equipment Co., Ltd. are introduced, then the technical standards and application of turbine flowmeter at home and abroad are compared in detail, and the differences between the standards are analyzed and evaluated. Finally, the work of Shanghai Orpheus in controlling the main technical performance of this series of turbine flowmeters is briefly introduced. Keywords: turbine flowmeter; Technical performance; With the rapid development of China's natural gas industry, the accuracy and reliability of natural gas trade measurement have attracted more and more attention from all walks of life. With the acceleration of China's integration with the international market, the use of low-precision flowmeters will be more and more restricted, and the demand for high-precision flowmeters will be very strong. The turbine flowmeter of Shanghai Aofei Gas Equipment Co., Ltd. (referred to as Shanghai Aofei for short) is put into development based on this market environment. Working principle and structural characteristics of 2 TGM series turbine flowmeter When the measured gas flows into the flowmeter, the gas is rectified and accelerated under the action of rectifier. Because the turbine blades form a certain angle with the gas flow direction, the force generated by the fluid drives the flowmeter turbine to rotate, and the theoretical rotation speed of the turbine is proportional to the flow rate. Working condition flow is read by turbine, movement, magnetic coupler (magnetic coupling), transmission mechanism and mechanical counter. The main structural components of TGM series gas turbine flowmeter (TGM-G400/ 100- 16) are shown in figure 1. TGM series turbine flowmeter adopts axial flow structure to meet the requirements of large range ratio, large pressure range and low pressure loss. The movement transmission adopts worm gear and worm transmission structure supported by closed double flange bearings, which reduces transmission loss and volume and improves structural strength; And a magnetic coupler (magnetic coupling) in radial magnetic coupling mode, which has the characteristics of small radial diameter and compact structure; The transmission mechanism is divided into two parts: independent transmission and independent counter, which is convenient to adjust the flow coefficient; In appearance, the lower shell as a support supports an independent transmission and an independent counter and counter panel; The transparent outer twelve sides of the upper shell intersect with the inclined plane, which is convenient to observe from the outside and has a unique shape; The rectifier adopts honeycomb structure, and the domestic patent number is (02280277.0), which bypasses the foreign patent barrier. The performance is mainly evaluated according to ISO 9951(GB/T18940-2003); Some parameters (durability, electrical connection, counter) refer to the standard of prEN 1226 1. At present, this series of products have obtained the national certificate of type approval of metrological products and the production license of metrological products. 1 mechanical counter 4 flowmeter body 2 magnetic coupling 5 rectifier device (patented product) 3 turbine 6 motion diagram 1 main structural parts of flowmeter 3 design standards and performance comparison of domestic and foreign turbine flowmeters 3. 1 international brands of gas turbine flowmeters, such as instromet in the Netherlands and elster in Germany, are all influential brands in the turbine flowmeter industry. In addition, there are some international famous brands such as Daniel and RMG, and the main design standard adopted is the European gas turbine flowmeter design standard prEN 1226 1. Because European standards have made more detailed provisions on user convenience and environmental protection. Therefore, it is also one of the most widely used standards in the world. Other standards for gas turbine flowmeters include AGA No7, ANSI/ASME MFC-4M, ISO995 1 (China people's national standard GB/T 18940 is equivalent to international standard ISO995 1) and so on. The detection conditions of these standards are very close to the main technical indicators, such as accuracy, stability, range ratio and so on. , and the provisions of prEN 1226 1 are more detailed in other indicators; Such as: durability requirements, mechanical counter requirements, etc. Table 1 is a comparison of several main parameters between European and American standards and national standards (international standards). 3.2 The main performance parameters of TGM series flowmeters of famous brands at home and abroad are compared with those of famous foreign turbine flowmeters such as Instromet, Elster, Equimeter, Daniel, Actoris and RMG. Figures 1, 2, 3 and 4 are performance curves with the same specifications as Instromet and Elster. From the data shown in Figure 2, Figure 3, Figure 4 and Table 2, it can be seen that the main parameters such as accuracy, linearity and range ratio are compared with similar products in advanced foreign countries, such as Instromet in the Netherlands (Figure 2); Shanghai offee TGM (Figure 4) still has a certain gap in accuracy and linearity, but it is very close to Elster (Figure 3) in Germany. On the whole, although there is a certain gap, it is already at the leading level in China. Domestic products are far behind foreign products in precision and range ratio, and most of them are not equipped with mechanical counters. The reading display is directly displayed by the flowmeter installed on the meter body. Users can't judge the gas flow in the pipeline through the operation of the mechanical transmission system of the turbine flowmeter, which limits users' choice of instruments, while TGM series turbine flowmeters are charged.